DELTA home

The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Aegopogon Humb. & Bonpl. ex Willd.

From the Greek aix (goat) and pogon (beard), referring to fascicles of awns.

~ Muhlenbergia sensu lato

Including Atherophora Steud., Hymenothecium Lag., Schellingia Steud.

Habit, vegetative morphology. Delicate annual. Culms 6–30 cm high; herbaceous. Leaves not basally aggregated; non-auriculate. Sheaths loose. Leaf blades linear; narrow; 1–2 mm wide; flat; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite, male-only, and sterile. The male and female-fertile spikelets mixed in the inflorescence (in triads, the central member hermaphrodite, the laterals male or sterile). The spikelets overtly heteromorphic.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the main axis bearing triplets of spikelets with short flat pedicels, the triplets short-pedunculate, spreading, the rachis filiform); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating; falling entire (i.e. the triplets falling). Spikelets in triplets; secund (the triplets on one side of the axis); sessile and pedicellate, or subsessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations, or unequally pedicellate in each combination (the central hermaphrodite spikelet sessile or subsessile, the reduced laterals pedicellate). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile.

Female-sterile spikelets. The longer-pedicelled male or neuter spikelets reduced.

Female-fertile spikelets. Spikelets 2 mm long; compressed laterally, or not noticeably compressed, or compressed dorsiventrally (?); falling with the glumes (the triplets disarticulating, with the pointed basal stipe). Rachilla terminated by a female-fertile floret.

Glumes present; two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; free; not pointed (apically notched); awned (via the extended midnerve); similar (membranous, truncate or notched, awned). Lower glume 1 nerved (?). Upper glume 1 nerved (?). Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas similar in texture to the glumes (membranous); not becoming indurated; incised; with a narrow, nerveless lobe outside each lateral awn; not deeply cleft; awned. Awns 3; median and lateral; the median similar in form to the laterals; continued from the nerve; non-geniculate (delicate); hairless (scabrous); much longer than the body of the lemma; entered by one vein. The lateral awns shorter than the median. Lemmas hairless; without a germination flap; 3 nerved. Palea present; relatively long (but somewhat shorter than the lemma); apically notched; awned (two-awned); textured like the lemma; not indurated; 2-nerved. Lodicules present; 2; fleshy; glabrous. Stamens 3. Anthers small. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit small (about 1.7 mm long in A. bryophylus); fusiform, or ellipsoid; compressed laterally. Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata (for the most part); consisting of one oblique swelling per cell (large). Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs present; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 30 microns long. Stomata common. Subsidiaries non-papillate; dome-shaped (sometimes approaching parallel). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent to imperfectly developed. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; confined to the central file(s) of the costal zones to present in alternate cell files of the costal zones; ‘panicoid-type’; cross shaped to dumb-bell shaped.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions absent. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (the large median cell of each group deeply inserted in the mesophyll). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the main bundles); forming ‘figures’ (the main bundles with anchors). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 3 species.

Distribution, phytogeography, ecology. Southern U.S.A. to Argentina.

Rusts and smuts. Rusts — Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: studied by us - A. cenchroides Willd.

Illustrations. • A. cenchroides: P. Beauv. (1812). • A. tenellus (Hitchcock and Chase, 1950)

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.